Small gas-turbine engines, which are typically run with small surge margins (i.e. relatively close to unsafe operating condition, in which the airflow through the compressors may be disrupted), can be disturbed by increasing the electrical load applied to a generator powered by said engines. This problem is compounded by the development of increasingly electrified aircraft. For example electrical fuel pumps, cabin environmental controls etc. can all place a large electrical load on the generator.
Conventionally, to counter the above, a large surge margin is applied to engine design which accommodates engine power off-takes and engine degradation. However, as more and more aircraft functions become electric (such as environmental cabin systems and de-icing mats) the potential for a large transient electrical load increases. Conversely, there is a desire to run the engine with a smaller surge margin as this improves the efficiency of the engine. Therefore there is a problem in that the engine either needs to be oversized (leading to inefficiency and increased weight) to effectively power-through transient loads, or the engine electronic control (EEC) needs to manage the loads before they occur and accommodate them accordingly. Thus a conventional approach is to indicate an impending load change via a discrete input from the aircraft to the EEC. However this may not resolve the problem, particularly if the electrical transient load is more rapid with respect to time than the capability of the engine to respond.